The TE01 mode, having advantages of field azimuthal symmetry and low propagating loss, is widely used in microwave applications, such as in gyrotron microwave sources. When applied to microwave plasma heating, the symmetrical distribution of the circular TE01 mode is expected to make heating more evenly.
Two methods have been classified to generate the TE01 mode with a cylindrical waveguide. One method is in-line coupling, and another is sidewall coupling. The former uses a deformed waveguide structure to convert a wave into the desired mode gradually. The transition length is generally long, and multiple modes could be excited during the converting process, wherein a Tantawi converter is commonly used. The latter, sidewall coupling, often uses a long and straight waveguide with coupling holes on the sidewall. Like the in-line converter, this type of converter needs converter components with longer lengths so that the electric wave can be converted slowly to the desired mode. However, during the converting process, the waves of the unwanted modes will interact with the electron beam, which will result in serious mode competition. Therefore, shortening the transition length and improving the mode purity could effectively lower the possibility of mode competition.
Thus, to overcome the aforementioned problems of the prior art, it would be an advancement in the art to provide an improved structure that can significantly improve the efficacy.
To this end, the inventor has provided the present invention of practicability after deliberate design and evaluation based on years of experience in the production, development and design of related products.